What You Need to Know About Car Fuses

Educational

Jan 11th, 2022

What You Need to Know About Car Fuses

Car fuses are tiny and cheap parts of your vehicle’s electrical system. Yet, these parts can shut down the entire system and potentially immobilise your car. So, what do you need to know about these components?

Automotive fuses are sacrificial devices that gets blown first when there’s an electrical fault, and thus, protect other components in the same circuit from electrical damage. Modern cars have more than 40 fuses organised in fuse boxes, typically in the engine bay or in the car’s cabin. 

Check your car user manual to be sure.

This guide covers everything you need to know about car fuses, from what they are to how they work. You’ll even discover how to troubleshoot and replace your blown fuses as well.

Let’s get started.

Part 1: All About Car Fuses

In this section, you’ll discover everything there is to know about automotive fuses. 

If you’re familiar with fuses in other electrical appliances and devices, then you’ll see that they’re similar in many ways. But if you’ve never seen, heard, or touched a fuse before, don’t worry! We’ve got everything you need to know about car fuses here.

What Are Automotive Fuses?

Automotive fuses are ‘sacrificial’ devices or components that play a critical role in your car’s electrical system. Cars have plenty of different electrical circuits functioning simultaneously, so you may be wondering how many fuses are in there. 

While older ones have fewer, it’s not unusual for newer models to have 40 fuses or more to protect their more advanced circuits.

How Do Automotive Fuses Work?

When there’s an electrical fault in any circuit, the fuse will blow itself to shut down the whole circuit before any severe damage can occur.

For example, if there’s a short circuit or power surge in your car, the wires could overheat and melt. Worse yet, electrical components like your radio or fan motor can also suffer damage, and a deadly electrical fire can start inside the vehicle.

Thanks to automotive fuses, they avert those things from happening. When a fuse blows, the circuit stops working. 

Unfortunately, you can’t repair or reuse a fuse, so you’ll have to replace it with a new one to restore the electrical circuit.

What Is a Fuse Box in a Car?

We’ve talked about 40 or more automotive fuses – that’s a lot! It would be a major headache if they were scattered all over your car’s bonnet and body. That’s why your car has a fuse box.

A fuse box is a protective case with a hard shell where you can find your car's fuses organised. 

Typically, one large-gauge wire leads into the fuse box carrying all the electricity in bulk. Then, that electric supply is split to supply all the different circuits, each with a fuse.

The number of fuse boxes and their locations is not the same across car brands and models. So, your car might have a single fuse box that houses all your vehicle’s fuses, or it might have two or more fuse boxes instead.

You will typically find these fuse boxes under the bonnet in the engine bay and the car’s interior.

To be sure, check your car’s user manual to locate and identify the fuse boxes you have onboard your vehicle.

What Does Each Fuse Do in a Car?

Each of the 40-or-so fuses protects an electrical circuit from electrical faults and prevents damage to any of its components.

If you’d like to know which car component a fuse is protecting, you’ll have to do a bit of detective work. First, you can check the car user manual. Manufacturers often assign a number to each fuse and list their purpose in the manual.

It's important to note that the number printed directly on the fuse is the amperage and not its specific use. You can check the box that the fuse came in to find the number pertaining to its use or purpose.

When there’s no information in the user manual, you can check inside the fuse box cover. That’s another standard location where manufacturers print details about the vehicle’s fuses, including each fuse’s amperage and type.

What Are the Types of Car Fuses?

Automotive fuses come in great variety. Generally, cars use a fuse known as a ‘blade fuse’. That’s why they look very different from other fuses you might be familiar with, like those used in your household.

Different Types of Automotive Fuses

  • Micro - The smallest type of car fuse, likely used for circuits with very low amperage levels.
  • Mini - A more compact blade fuse that helps to save space, sometimes featured in smaller fuse boxes.
  • Standard - The most common type of car fuse you’ll see. Your vehicle likely has many of these.
  • Maxi - A heavy-duty fuse for a car circuit with higher amperage.

As you can see, the types of blade fuses in your car differ by size and capacity. Since your car’s electrical system powers all sorts of different devices, you’ll likely find a combination of several fuse types in your fuse box.

What Are Automotive Relays and Diodes?

Automotive relays and diodes are not the same as car fuses. Still, they work alongside fuses, and you’ll likely find them if you’re ever troubleshooting your car’s electrical system.

So, here are the basics of what you need to know:

  • Automotive relay: Relays are electrically-powered switches that control the supply of power. For example, suppose your car’s computer wants to power a particular component, it’ll trigger the relay to supply power to that part.
  • Automotive diode: Diodes ensure that electrical power only flows one way, so it also protects the electrical circuit.

Can You Drive a Car with Missing Car Fuses?

Maybe. Remember that each car fuse keeps an electrical circuit closed and functioning. So, you can get away with missing a few car fuses unless they connect to your car’s most critical functions.

Suppose you’re missing any of the fuses related to your car’s ignition system. In that case, your vehicle can’t start at all. 

On the other hand, a missing headlight fuse won’t immobilise your car (though that’s still a safety hazard).

Part 2: Troubleshooting Car Fuses

Now that we’ve explored the basics of car fuses, Part 2 of this guide will explore how you can troubleshoot them.

Symptoms of a Bad Car Fuse

Of all the car parts people check regularly, car fuses are rarely among them. That’s entirely normal, so don’t feel bad if you don’t even know how to open a fuse box.

Typically, people only check their fuses when symptoms start showing.

What Are Signs and Symptoms of a Blown Fuse?  

The signs you should look out for are related to your vehicle’s electrical system, including:

  • Loss of power (the most direct symptom): A blown fuse will cut its circuit entirely, preventing any electricity from flowing through it. Electrical components, like a lightbulb, fan motor, or radio, will stop working and won’t turn on.
  • Burnt smell, flickering lights (indirect symptoms): Some symptoms of a lousy car fuse aren’t as direct as a loss of power. For example, burning smells and flickering lights suggest an electrical fault or that the wires are overheating and melting. The affected fuse could blow at any moment.

How to Check Car Fuses

When you suspect that there’s a problem with your car fuses, you must take precautions before you begin troubleshooting.

Remember: You’re dealing with an electrical system. Even though that system is powered only by your car’s battery, that’s still enough electricity to put you in danger. So, shut off the engine and disconnect the battery before troubleshooting or doing repairs.

Once it’s safe to check your fuses, here’s what you can do:

  1. Firstly, locate the fuse boxes in your car (if there’s more than one). Keep the user manual close by for quick reference.
  2. Then, open the fuse box cover and read any diagrams or lists printed inside it.
  3. If you know which electrical circuit is affected (say, your cigarette lighter stopped working), refer to the user manual and diagrams to locate the relevant fuse.
  4. If you don’t know which circuit is affected, you’ll have to remove fuses individually and inspect each one. Again, it helps if you start by looking for noticeable burn marks or smells to confirm if a fuse has blown.
  5. When you find a blown fuse, replace it with a new one. Important: Make sure that the amperage of the new fuse is the same with the one you’re replacing.
  6. Cover the fuse box and reconnect your battery when you’re all done. Then test the affected circuit (for this example, check that your cigarette lighter is working again).

How Do You Know a Fuse Is Blown?

There are 3 methods you can use to confirm that a fuse is blown:

Method 1: Visible Damage

Check the fuse for any visible signs of damage. A blown fuse will often have burn marks on them, particularly around its metal prongs. You might also notice some melting on its plastic parts. Besides that, the fuse will have a burnt smell coming from it.

These are sure signs of a blown fuse, and it means you’ll need a new one.

Method 2: Shine a Light

We’ve seen many times in this guide that a blown fuse will break the circuit. But how does that happen? 

Well, there’s a wire in the fuse that conducts electricity. That wire will break when the fuse blows, and no electricity can flow through the fuse.

So, if there are no signs of visible damage on the fuse’s outside, check that wire inside instead. Then, shine a light through the fuse and check if the wire is intact. If it’s broken, the fuse is blown, and you’ll have to replace it.

Method 3: Use a Multimeter

If you have a multimeter lying around your house somewhere, you can use that to check for continuity in the fuse (i.e., check that electricity can flow through it). 

So, even if the fuse somehow looks perfectly fine, a multimeter is the most reliable way to test it. The fuse might be faulty, even though it hasn’t blown, burnt, or melted.

Why Do Car Fuses Blow?

Replacing a blown fuse will solve your problems, but it can be quite a frustrating mystery as to why you need to replace them at all. 

If your fuses keep blowing, it’s important to know what causes it. A few reasons your car fuses are blown are:

  • Damaged or exposed wiring: The first reason your car fuses blow is that there’s damaged or exposed wiring somewhere in the vehicle. That can cause voltages to spike, triggering the fuses to blow.
  • Defective motors or componentsElectrical problems with other components like wiper or fan motors can also cause fuses to blow. For example, a malfunctioning motor might draw or pull in too much electricity (that’s bad!), causing the fuse to blow.
  • Short-circuits: A short-circuit is when electricity flows to an unintended path. That’s dangerous because it can damage your car’s electrical and electronic components, and yes, you guessed it – it can cause a fuse to blow.
  • Power surges: Last but not least, a power surge can also blow fuses. One thing that causes a surge is the damaged wiring mentioned earlier. As a protective measure, the fuse will blow and cut the circuit.

Why Does My Car Keep Blowing Fuses?

One crucial thing to remember is that a blown fuse is a symptom and not the root problem. It’s totally normal for a couple of fuses to blow over the years. 

However, if the same fuse keeps blowing time and time again, that’s a clear sign that there’s a problem in that particular circuit.

So, before you send yet another fuse to its inevitable death, you must troubleshoot the entire circuit. Look for wiring issues or faulty components and resolve those first. Only then can you replace the fuse and expect it to last long.

What Fuse Do I Need for My Car? Or Can I Replace a Fuse Myself?

Yes, you can replace the fuses in your car by yourself. First, however, there are two things you must know:

  • Firstly, keep the car off and disconnect the battery. That way, you won’t shock yourself as you troubleshoot or replace those fuses.
  • Secondly, it's best to get the exact same type of fuse. That means buying a replacement that's the same type, size, and - the most critical - the same amperage.

Making a mistake with your car’s electrical system can get you hurt or cost you money if there’s further damage. So, if you’re not sure or confident about what you’re doing, it’s always best to hire a mechanic or auto electrician to do it for you.

If you’re in the market for new car fuses, or you’re looking for a workshop to help you troubleshoot your car’s electrical system, check out our Directory at CarPart AU. It’s your handy link to the nearest workshops in your location, wherever you are in Australia.


By Ray Hasbollah